Optoelectronic position detecting devices detect the absolute position and movement of specific machine parts with respect to each other. For example, optoelectronic position detecting devices detect robot movements. Optoelectronic position detecting devices are used in the automotive industry, for example, for detecting steering angles. The steering angle and the steering angle lock in motor vehicles is required by a driving dynamics control system. In addition to the steering angle values, the driving dynamics control system obtains further measurement data such as wheel rotational speed and the rotation of the motor vehicle about its vertical axis. The driving dynamics control system evaluates the absolute steering angle lock and the steering speed with other detected data for generating control signals. The control signals control actuators such as brakes and are used for engine management.
DE 40 22 837 A1 discloses an optoelectronic steering angle sensor. The steering angle sensor includes a light source and a line sensor arranged in parallel and spaced apart from each other to form a gap. A round encoder disc engages into the gap and is non-rotatable connected to the steering spindle. A code transmitter is formed as a light slit disc having a code trace. The code trace is a spiral which increases in size from the inside outwards. A CCD-sensor line is the line sensor. Because of the exposure of the image points of the line sensor in the case of a specific steering lock, it is possible to obtain information regarding the steering angle lock.
Steering angle sensor systems are installed in the region of the steering spindle of the motor vehicle. The installation space available in this region for installing steering angle sensor systems is limited. The available installation space is particularly limited in the axial direction of the steering spindle. The steering angle sensor of DE 40 22 837 A1 does not satisfy the demands of the minimum installation space. A line-source-LED is located as the light source on one side of the encoder disc on a plate and the sensor line is located on another plate on the other side of the encoder disc. The installation space is determined by the structure of the electronic components on the two plates and the width of the gap provided between these two electronic elements. The gap must be sufficiently large to ensure that the encoder disc can be rotated therein with a sufficient degree of axial play.
DE 36 41 288 C1 discloses an optoelectronic position detecting device requiring a smaller installation space than the required installation space of the device disclosed in DE 40 22 837 A1. The light source and the sensors of this device are located on the same side of the encoder disc. The encoder disc is essentially impervious to light on its side pointing towards the light source and the sensor elements. An annular light coupling window is exposed only in the region of the rotational center of the encoder disc. Accordingly, windows are provided in the light-impervious layer. The windows decouple the light from the encoder disc.
DE 36 41 288 C1 discloses another embodiment of the optoelectronic position detection device in which light is coupled from the side over the peripheral surface of the encoder disc. However, the problem associated with such an arrangement is that the encoder disc can only have a single trace.
DE 86 21 057 U1 discloses an optoelectronic angle measuring device requiring a small amount of installation space. The required amount of installation space is small because the encoder disc includes an annular recess into which a fixed light source protrudes. The light emitted by the light source is coupled by the annular recess into the encoder disc. The light is then reflected on a curved, metallized peripheral surface towards the planar base surface of the encoder disc such that the coding provided on this side of the encoder disc is exposed to light. However, this optoelectronic position detecting device has the problem that it is not possible to expose a plurality of code traces to a sufficient quantity of light.